Unveiling a Surface Electronic Descriptor for Fe–Co Mixing Enhanced the Stability and Efficiency of Perovskite Oxygen Evolution Electrocatalysts
Yongchul Kim, Miran Ha, Rohit Anand, Mohammad Zafari, Jeong Min Baik, Hyesung Park, Geunsik Lee
Abstract
The influence of cation mixing on the oxygen evolution reaction (OER) activity of a LaxSr1–xCoyFe1–yO3 (LSCF) double perovskite is investigated using density functional theory (DFT) calculations. The O 2p band center (E2p) has a good linear relation with the binding energy of the OER intermediate species when the chemical composition is varied by only the x or y value, but this relation is insufficient for describing the nonmonotonic behavior over the entire x and y ranges. Based on the projected density of states and wavefunction analysis, the minority spin dxy electrons of surface layer metal atoms are significant due to their stability, where the antibonding states between dxy and the lattice oxygen p become occupied when Co atoms with one d electron more than Fe are present. Thus, by additionally considering the dxy band center, a surface electronic descriptor (E2p – 0.4Edxy) excellently describes the binding energy of the OER intermediates and the stability against oxygen-vacancy formation, which also explains the enhanced OER stability and efficient Fe–Co mixing. Our study unveils the key mechanism of the excellent OER performance and high stability of previously reported LSCF materials as well as provides heterostructure engineering guidance for optimal surface electronic structures.